The present invention relates to a method and apparatus for measuring the height of a stream consisting of tobacco or the like. More particularly, the invention relates to a method and apparatus for ascertaining the height of a relatively narrow stream consisting of particulate fibrous material. Still more particularly, the invention relates to a method and apparatus for monitoring one transverse dimension of a continuously moving stream of discrete particles, e.g., a stream of tobacco shreds which contains a surplus of tobacco and is about to be trimmed prior to draping into a web of cigarette paper or the like. The resulting rod, wherein a rod-like filler of fibrous material is confined in a tubular wrapper, is thereupon severed to yield a succession of discrete rod-shaped sections, e.g., plain cigarettes of unit length.
The term "fibrous material" is intended to embrace shreds or other fragments of natural or reconstituted tobacco, shreds or other fragments of tobacco substitutes, mixtures of natural, reconstituted and/or substitute tobacco as well as filter material for use in filter mouthpieces or filter plugs for cigarettes or the like. For the sake of simplicity, the invention will be described with reference to the manufacture of plain cigarettes; however, it will be understood that the invention can be practiced also in connection with the making of filter cigarettes, plain or filter tipped cigars or cigarillos, and filter plugs.
The manufacturers of cigarettes strive to obtain a rod-like tobacco filler of uniform density (hardness), i.e., it is desirable to insure that the so-called filling force of the fillers of each of a long series of cigarettes will match or closely approach an optimum value. So-called "densely packed" cigarettes are preferred by a large majority of smokers. As a rule, the distributor of a cigarette making machine delivers particles of tobacco to the stream forming zone at a rate exceeding the requirements of the filler, i.e., the tobacco stream contains a surplus of tobacco and such surplus is removed during conversion of the stream into an equalized stream which, in turn, is compacted and thereby converted into a rod-like filler. One side of the stream which is transported past the trimming or equalizing device is exposed, and such exposed side exhibits more or less pronounced hills and valleys. The minimum height of the tobacco stream in the deepmost region of the deepest valley must still exceed (or cannot be less than) the desired height of the equalized stream. The development of hills and valleys at the exposed side of the stream cannot be avoided for a number of reasons, especially owing to the nature of tobacco. Thus, the shreds include short and long particles some of which are straight and some of which exhibit a pronounced crimp. Moreover, the particles are likely to be interlaced with each other to form clumps regardless of the fact that a modern distributor which feeds tobacco particles to the stream building zone of a cigarette maker embodies several devices whose function is to prevent the agglomeration of particles or to break up such accumulations ahead of the stream building zone.
The trimming or equalizing device is adjustable so that its knife or knives can remove larger or smaller quantities of tobacco at the exposed side or surface of the stream. Since the trimming invariably entails the formation of less satisfactory short tobacco and tobacco dust, it is desirable to form a tobacco stream which requires a minimum of trimming. Attempts to reduce the surplus in the untrimmed tobacco stream include the provision of means for preventing the formation of pronounced hills and valleys at the exposed side of the stream and/or for shifting the material from the hills into the valleys. As a rule, the removed surplus is returned into the magazine of the distributor where it increases the percentage of less desirable short tobacco.
It is already known to regulate the feed of tobacco to the stream building zone and the operation of the trimming device in dependency on a variety of parameters including the filling force of the filler in a continuous cigarette rod, the density of tobacco in the wrapped filler, the diameter of the filler and/or the corresponding characteristics of the stream ahead of the wrapping station. A drawback of such proposals is that they fail to take into consideration the geometric shape of the stream ahead of the trimming device, especially the configuration of the exposed surface of the stream, i.e., the configuration of that surface from which the knife or knives of the trimming device remove the surplus. In other words, presently known apparatus are not designed to influence the formation of an equalized tobacco stream in dependency on that parameter (i.e., the configuration of the exposed surface of the untrimmed stream) which controls the amount of removed surplus and thereby determines the quantity of short tobacco which is the byproduct of the trimming operation. As mentioned above, the development of hills and valleys is attributable to a host of factors including fluctuations in the rate of delivery of tobacco to the stream forming zone, the design of the stream forming zone, the configuration and size of tobacco particles, the nature of tobacco, the manner in which the particles of tobacco were conditioned prior to admission into the magazine of the distributor, the construction of the distributor, the nature of tobacco fibers, the magnitude of the force (suction) which attracts tobacco particles to the conveyor in the stream building zone and/or others.
British Pat. No. 1,468,,169 discloses a mechanical sensor which rides on the uneven exposed surface of a moving tobacco stream. The sensor compacts the stream and initiate the generation of signals indirectly denoting the height of successive increments of the untrimmed stream, i.e., the distance between the exposed side and the conveyor or conveyor portion supporting and advancing that side of the stream which is located opposite the uneven exposed side. The purpose of the sensor is to allow for calculation of the resistance which the stream offers to deformation, and the thus obtained signals are utilized to effect adjustments of the trimming device.